I have an Asterisk 11 system out on the internet and 2 Digium D40 phones connecting to it on seperate internet connections and ISP's

The first phone connects fine to Asterisk through my home internet connection and NATThe secound phone is on a company fiberconnection (and other then NAT they say there should be no restrictions in place)

But the other phone seams to have problems. It does register with the Asterisk serverBut it keeps falling out and. If I make a call from the secound phone, the other phone rings, but no audio either direction, and Asterisk terminates the call after a few secounds.If I call the secound phone it rings and the same problem with audio and disconnect.